Bis-pyrazoles as antifoggants for photographic silver halide emulsions



Unitcd States Patent() 3,106,467 BlS-PYRAZOLES AS ANTIFOGGANTS FOR PHOTO- GRAPHIC SILVER HALIDE EMULSIONS Charles F. H. Allen and Burton D. Wilson, Rochester,

N.Y., assignors to Eastman Kodak Company, Rochester, N.Y., a corporation of New Jersey No Drawing. Filed Oct. 19, 1960, Ser. No. 63,432

9 Claims. (Cl. 96-109) This invention relates to fog inhibitors or stabilizers for photographic silver halide emulsions and to photo graphic silver halide emulsions containing them.

It is well known that photographic emulsions on storage tend to lose sensitivity and to become spontaneously developable without exposure to light. There is normally a detectable amount of the silver salt reduced during development in the areas where no exposure was given; this is commonly called fog, and sometimes called chemical fog where it is necessary to distinguish between it and the effects of accidental exposure to radiation; in this invention, we are not concerned with the latter.

Fog depends both on the emulsion and the conditions of development; for a given emulsion it increases with the degree of development. With constant development conditions, it tends to increase with time, temperature and relative humidity of storage conditions; it is common practies to make accelerated tests of the stability of photographic emulsions by storage at increased temperature or humidity, 01' both. It is, oi course, desirable to have emulsions as stable as possible under the conditions of high temperature and humidity which may occur in tropical climates, for example. Fog usually appears over the whole area of the sensitive coating, but when severe, it frequently is non-uniform. Fog may also be caused by exposure to chemicals, for example, hydrogen sulfide and other reactive sulfur compounds, hydrogen peroxide vapor, and strongly reducing material. While antifoggants and stabilizers may protect, to some extent, against such effects, it is normally understood that an antifoggant protee-ts against spontaneous growth of fog during prolonged storage or storage at high temperatures and humidities, or during development to maximum contrast and speed, or both. i

It is, accordingly, an object of our invention to provide a method tor stabilizing photographic emulsions. A further object of our invention is to maintain the sensitivity and fog of silver halide emulsions at or close to initial optimum values under keeping conditions of high temperature and humidity. A further object is to provide photographic silver halide emulsions containing antifoggants or stabilizers. Other objects will become apparent from a consideration of the following descriptionand examples.

The above objects are accomplished by adding to the photographic silver halide emulsion, generally in the form of a solution in an organic solvent, a cmp und selected from those represented by the following general formula:

carbanilyl, etc.), etc., R represents an alkylene group or 3,106,467 Patented Oct. 8, 1963 an arylene group (e.g., methylene, ethylene, trimethylene, tetramethylene, pentamethylene, hexamethylene, heptamethylene, decamethylene, methyl-substituted ethylene, ethyl-substituted ethylene, phenylene, tolylene, ethylphenylene, etc.), and n represents a positive integer of from 1 to 2.

Bisepyrazoles embraced by the above general formula which are especially useful in practicing our invention include those represented by the following general formula:

wherein R and it each have the values given above, R and R each represents a hydrogen atom or a lower alkyl group (e.g., methyl, ethyl, n propyl, n-butyl, etc.) and R represents a hydrogen atom, a lower alkyl group :(e. g., methyl, ethyl, n-propyl, n-butyl, etc.), or a carbamy-l group (e.g., canbamyl, N-alkylcarbamyl, such as N-methylcarbamyl, N-ethylycarbamyl, etc., N-arylcar'barnyl, such as carbanilyl, etc.).

Another group of bis-pyrazole compounds uset'ul in practicing our invention are those represented by the following general formula:

wherein R and R R and n each have the values given above.

It has been previously suggested in the prior art that monopyrazole compounds can be employed to stabilize photographic silver halide emulsions. See Sheppard and Wightman US. Patent 1,763,989, issued June 17, 1930.

However, we have found that the bis-pyrazole compounds of the present invention are markedly superior to the monopyrazole compounds suggested by this patent. The substantial increase in antifoggant activity provided by our bis-pyrazole compounds is illustrated below.

The cfog inhibitors which we propose to use are added to the emulsion during the process of manufacture, t avoid loss of sensitivity and to inhibit the growth of fog with passage of time under non-ideal conditions of storage.

A solution of the compounds of the invention when added in suitable concentration, ibefore coating, to unsensi-tized, chemically sensitized, or optically sensitized photographic emulsions does not appreciably aifect the sensitornetric values for sensitivity and fog when measurements are made soon after coating. When sensitometric measurements are made at appreciable intervals of time, at elevated temperatures and dry or somewhat humid conditions these compounds do stabilize photographic speed and maintain fog at a low level.

The preparation of silver halide emulsions involves three separate operations: (1) the emulsification and digestion or ripening of the silver halide, (2) the freeing of the emulsion from excess soluble salts, usually by washing, and (3) the second digestion or after-ripening to obtain increased sensitivity. (Mees, The Theory of the Photographic Process, (1942).) We prefer to add the fogis inhibiting agents after the final digestion or after-ripening, although they can advantageously be added prior to digestion.

The bis-pyrazole compounds useful in practicing our invention can advantageously be prepared according to methods which have been previously described in the prior art. Many of the bis-pyrazole compounds useful in our invention have been previously prepared and their properties have been described in the technical literature. Other members of the series have not been previously prepared or described in the literature, although the methods of preparing these new compounds follow procedures which have been previously described in detail by those skilled in organic synthesis. A particularly useful method of preparing many of the bis-pyrazole compounds of our invention comprises reacting hydrazine or a substituted hydrazine base with a compound containing four carbonyl groups. In order to form the pyrazole ring, it is obvious that these four carbonyl groups are divided into groups of two and that the carbonyl groups of the latter are separated from one another by a single carbon atom. Thus it is possible to form the S-membered pyrazole ring. In many instances, the hydrazine base reacts spontaneously with the tetracarbonylic compound and it is sometimes necessary to actually cool the reaction mixture in order to prevent too violent a reaction. In some instances the reaction proceeds less rapidly and it may be advisable to accelerate the reaction, once the initial reaction has subsided, by the application of heat. A small amount of water added to the reaction mixture seems to increase the rate of reaction and this is illustrated in the following examples. Typical hydrazine bases which can be employed in this reaction include hydrazine itself and the monoalkyl and monoaryl hydrazine bases, such as methylhydrazine, ethylhydrazine, propylhydrazine, phenylhydrazine, tolylhydrazine, etc. The following examples will serve to illustrate the synthesis of the hispyrazole compounds which can be employed in our invention.

EXAMPLE 1.--5,5'-DIMETHYL-3,3-BIPYRAZOLYL To a stirred mixture of 8 ml. of 95+ percent hydrazine and 0.8 ml. of water, were added 4.25 g. of 2,4,5,7-octanetetrone in small portions as rapidly as the exothermic reaction allowed. The mixture was cooled and the solids were collected, washed with water and dried, to give a crude yield of 4.01 g. Two recrystallizations from aqueous methanol, using carbon once, yielded 1.7 g. of slightly yellowish crystals, M.P. 284-286" C. (dec.) (corr.). (Literature, M.P. 286 C.R. Fusio and S. Zumin, Gazz. chim. Ital, 76, 223 (1946).)

EXAMPLE 2.-3,3,5,5-TETRAMETHYL-4,4-

BIPYRAZOLYL EXAMPLE 3.--3,3',5,5'-TETRAETHYL-4,4- BIPYRAZOLYL By a procedure like that of Example 1, 10.2 g. of 4,5- dipropionyl-3,6-octanedione were added to a mixture of 12 ml. of 95+ percent hydrazine and 2 ml. of water. The yield of crude produce was 6.57 Recrystallization from aqueous ethanol gave 6.2 g. of colorless crystals, M.P. 249251 C. (corr.).

Analysis.Calcd. for C H N C, 68.26; H, 9.00; N, 22.74. Found: C, 68.0; H, 9.3; N, 22.4.

EXAMPLE 4.-M ETHYLENE4,4- IS 3,5- DIMETHYLPYRAZOLE By a procedure like that of Example 1, 7.16 g. of 3,5- diacetyl-2,6-heptanedione were added to a mixture of 9 ml. of percent hydrazine and 1 ml. of water. The yield of crude product was 4.06 g. Recrystallization from aqueous methanol gave 3.52 g. of colorless crystals, M.P. 285287 C. (corr.). (Literature, M.P. 286 C.-P. Rabe and F. Elze, Ann, 323, (1902).)

Anaiysis.-Calcd. for C I- 19 C, 64.68; H, 7.89; N, 27.43. Found: C, 64.9; H, 8.0; N, 27.3.

EXAMPLE 5.1,1',3,3',5,S HEXAMETHYLAA BIPYRAZOLYL To a solution of 28.8 g. of mcthylhydraziuc sulfate in 50 mi. of water was added concentrated ammonium hydroxide to the Congo Red end-point. To this solution were added 17.2 g. of 3,4-diacetyl-2,5-hexanedione and 50 ml. of ethanol. The resulting mixture was heated under reflux for five hours and cooled. The solids were collected, washed with water, and dried to recover 8.3 g. of 3,4-diacetyl-2,S-hexanedione. The combined filtrate and washings were made strongly alkaline, whereupon phase separation occurred. The mixture was extracted with ether and worked up to yield 9.0 g. of a yellow residue. Three recrystallizations from water (using carbon once) gave 4.2 g. of colorless crystals, M.P. 89-90 C. (corr.).

Analysis.Calcd. for C H N C, 66.03; H, 8.31; N, 25.67. Found: C, 66.0;1-1, 8.6; N, 25.9.

EXAMPLE 6.METHYLENE-4,4-BIS-( 1, 3, 5- TRIMETHYLPYRAZOLE) By a procedure like that of Example 5, but using 75 ml. of water, 30 ml. of ethanol, and 21.2 g. of 3,5- diacetyl-2,6-heptancdione, there was obtained a solution which was heated under reflux for six hours, cooled, made strongly alkaline, and the crude product collected (22.0 g.). Two recrystallizations from water gave 16.4 g. of colorless crystals, M.P. 71.5-72 C. (corr.).

AI1alysis.-Calcd. for C H N C, 67.20; H, 8.68; N, 24.12. Found: C, 66.8; H, 9.0; N, 23.7.

By a. procedure like that of Example 5, but using half the quantities and 8.51 g. of 2,4-,5,7-octanetetrone, there was obtained a solution which was heated under reflux! for four hours, cooled, made strongly alkaline, and the crude produce collected (18.5 g.). This residue was digested with 400 m1. of boiling water, filtered hot, and cooled. The precipitate was recrystallized several times from aqueous methanol, yielding 2.5 g. of colorless crystals, M.P. 246--246.5 C. (corr.).

Analysis-Calcd. for C H N C, 63.13; H, 7.42; N, 29.45. Found: C, 63.3; H, 7.5; N, 29.8.

The photographic emulsions used in practicing our invention are of the developing-out type.

The emulsions can be chemically sensitized by any of the accepted procedures. The emulsions can be digested with naturally active gelatin, or sulfur compounds can be added such as those described in Sheppard U.S. Patent 1,574,944, issued March 2, 1926, Sheppard et al. U.S. Patent 1,623,499, issued April 5, 1927, and Sheppard et al. U.S. Patent 2,410,689, issued November 5, 1946.

The emulsions can also be treated with salts of the noble metals such as ruthenium, rhodium, palladium, iridium, and platinum. Representative compounds are ammonium chloropalladate, potassium chloroplatinate, and sodium chloropalladite, which are used for sensitizing in amounts below that which produces any substantial fog inhibition, as described in Smith and Trivelli U.S. Patent 2,448,060, issued August 31, 1948.

The emulsions can also be chemically sensitized with gold salts as described in Waller et al. U.S. Patent 2,399,083, issued April 23, 1946, and Damschroder et a1. U.S. Patent 2,642,361, issued June 16, 1953. Suitable compounds are potassium chloroaurite, potassium aurithiocyanate, potassium chloroaurate, auric trichloride and 2-aurosulfobenzothiazole methochloride.

The emulsions can also be chemically sensitized with reducing agents such as stannous salts (Carroll U.S. Patent 2,487,850, issued November -15, 1949), polyamines, such as diethylene triarnine (Lowe and Jones U.S. Patent 2,518,698, issued August 15, 1950), polyamines, such as spermine (Lowe and Allen US. Patent 2,521,925, issued September 12, 1950), or bis(fi-aminoethyl) sulfide and its Water-soluble salts (Lowe and Jones U.S. Patent 2,521,926, issued September 12, 1950).

The emulsions can also be optically sensitized with cyanine and merocy-anine dyes, such as those-described in Brooker U.S. Patents 1,846,301, issued February 23, 1932; 1,846,302, issued February 23, 1932; and 1,942,854, issued January 9, 1934; White U.S. Patent 1,990,507, issued February 12, 1935; Brooker and White U.S. Patents 2,112,140; issued March 22, 1938; 2,165,338, issued July 11, 1939; 2,493,747, issued January 10, 1950 and 2,739,964, issued March 27, 1956; Brooker and Keyes U.S. Patent 2,493,748, issued January 10, 1950; Sprague U.S. Patents 2,503,776, issued April 11, 1950 and 2,519,- 001, issued August 15, 1950; Heseltine and Brooker U.S. Patent 2,666,761, issued January 19, 1954; Heseltine U.S. Patent 2,734,900, issued February 14, 1956; Van Lare U.S. Patent 2,739,149, issued March 20, 1956; and Kodak Limited British Patent 450,958, accepted July 15, 1936.

The emulsions may also contain speed increasing compounds of the quaternary ammonium type of Carroll U.S. Patent 2,271,623, issued February 3, 1942; Carroll and Allen U.S. Patent 2,288,226, issued June 30, 1942; and Carroll and Spence U.S. Patent 2,334,864, issued November 23, 1943; or the polyethylene glycol type of Carroll and Beach U.S. Patent 2,708,162, issued May 10, 1955; or the quaternary ammonium salts and polyethylene glycols of Piper U.S. Patent 2,886,437, issued May 12, 1959; as well as the thiopolymers of Graham and Sagal U.S. application Serial No. 779,839, filed December 12, 1958 (now U.S. Patent 3,046,129, issued July 24, 1963), and the Dann and Chechak U.S. application Serial No. 779,874, filed December 12, 1958 (now U.S. Patent 3,046,134, issued July 24, 1 962).

The emulsions may contain a suitable gelatin plasticizer such as glycerin; a dihydroxy alk-ane such as 1,5- pentane diol as described in Milton and Murray U.S. application Serial No. 588,951, filed June 4, v1956 (now U.S. Patent 2,960,404, issued November 15, 1960); an ester \Of an ethylene bis-glycolic acid such as ethylene bis(methyl glycolate) as described in Milton U.S. Patent 2,904,434, issued September 15, 1959; bis-(ethoxy diethylene glycol) succinate as described in Gray U.S. application Serial No. 604,333, filed August 16, 1956 (now U.S. Patent 2,940,854, issued June 14, 1960), or a polymeric hydrosol as results from the emulsion polymerization of a mixture of an amide of an acid of the acrylic acid series, an acrylic acid ester and a styrenetype compound as described in Tong U.S. Patent 2,852,- 386, issued September 16, 1958. The plasticizer may be added to the emulsion before or after the'addition of a sensitizing dye, if used.

The emulsions may be hardened with any suitable hardener for gelatin such as formaldehyde; a halogensubstituted aliphatic acid such as mucobromic acid as described in White U.S. Patent 2,080,019, issued May 11, 1937; a compound having a plurality of acid anhydride groups such as 7,8-diphenylbicyclo(2,2,2)-7-octene-2,3, 5,6-tetra-carboxylic dianhydride, or a dicarboxylic or a disulfonic acid chloride such as terephthaloyl chloride as described in Allen and Carroll U.S. Patents 2,725,294, and 2,725,295,both issued November 29, 1955; a cyclic 1,2-diketone such as cyclopentane-1,2-dione as described in Allen and Byers U.S. Patent 2,725,305, issued Novemher 29, 1955; a bisester of methane-.sulfonic acid such as 1,Z-di-(methanesulfonoxy)-ethane as described in Allen and L-aakso U.S. Patent 2,726,162, issued December 6, 1955; 1,3-dihydroxym-ethylbenzimidazol-Z-one as described in July, Knott and Pollak U.S. Patent 2,732,316, issued January 24, 1956; a dialdehyde or a sodium bisulfite derivative thereof, such as B-methyl glutaraldehyde bis-sodium bisulfite as described in Allen and Burness U.S. patent application Serial No. 556,031, filed December 29, 1955 (now abandoned); a bis-aziridine carboxamide such as trimethylene bis(1-aziridine carboxamide) as described in Allen and Webster U.S. patent application Serial No. 599,891, filed July 25, 1956 (now U.S. Patent 2,950,197, issued August 23, 1960); 2,3-dihydroxy dioxane as described in Jeffreys U.S. Patent 2,870,013, issued January 20, 1959; or bisisocyanate as described in Henn et a1. U.S. patent application Serial No. 805,357, filed April 10, 1959.

The emulsions may contain a coating aid such as saponin; a lauryl or oleyl monoether of polyethylene glycol as described in Knox and Davis U.S. Patent 2,831,766, issued April 22, 11958; a salt of a sulfated and alkylated polyethylene glycol ether as described in Knox and Davis U.S. Patent 2,719,087, issued September 27, 1955; an

' acylated alkyl taurine such as the sodium salt of N-oleoyl- N-rnethyl taurine as described in Knox, Twardokus and Davis U.S. Patent 2,739,891, issued March 27, 1956; the reaction product of a dianhydride of tetracarboxybutane with an alcohol or an aliphatic amine containing from 8 to 18 carbon atoms which is treated with a base, for example, the sodium salt of the monoester of tetracarboxybutane as described in Knox, Stenberg and Wilson U.S. Patent 2,843,487, issued July 15, 1958; a watersoluble maleopimarate as described in Knox and Fowler U.S. Patent 2,823,123, issued February 11, 1958; an alkali metal salt of a substituted amino acid such as disodiurn N- (carbo-p-tert.-octylphenoxypentaethoxy) -glutamate as described in Knox and Wilson U.S. patent application Serial No. 600,679, filed July 30, 1956 (now U.S. Patent 3,038,804, issued June 12, 1962); or a sulfoa succinamate such as tetrasodium N-(1,2-dicarboxyethyl)- Naoctadecyl sulfosuccinamate as described in Knox and Stenberg U.S. patent application Serial No. 691,125, filed October 21, 1957 (now U.S. Patent 2,992,108, issued July 11, 1961), or a sodium salt of an alkylarylpolyether sulfonate of Baldsiefen U.S. Patent 2,600,831, issued June 17, 1952. r

The addenda which we have described may be used in various kinds of photographic emulsions. In addition tobeing useful in X-ray and other nonoptically sensitized emulsions they may also be used in orthochromatic, panchromatic, and infrared sensitive emulsions. They may be added to the emulsion before or after any sensitizing dyes which are used. Various silver salts may be used as the sensitive salt such as silver bromide, silver iodide, silver chloride, or mixed silver halides such as silver chlorobromide or silver bromoiodide. The agents may be used in emulsions intended for color photography, for example, emulsions containing color-forming couplers or emulsions to be developed by solutions containing couplers or other color-generating materials, emulsions of the mixed-pacl et type, such as described in Godowsky US; Patent 2,698,794, issued January 4, 1955; or emulsions of the mixed-grain type, such as described in Carroll and Hanson U.S. Patent 2,592,243, issued April 8, 1952. These agents can also be used in emulsions which form latent images predominantly on the surface of the silver halide crystal or in emulsions which form latent images predominantly inside the silver halide crystal, such as those described in Davey and Knott U.S. Patent 2,592,250, issued April 8, 1952.

These may also be used in emulsions intended for use in diffusion transfer processes which utilize the un developed silver halide in the nonimage areas of the negative to form a positive by dissolving the undeveloped A silver halide and precipitating it on a receiving layer in close proximity to the original silver halide emulsion layer. Such processes are described in Rott US. Patent 2,352,014, issued June 20, 1944, and Land US. Patents 2,584,029, issued January 29, 1952; 2,698,236, issued December 28, 1954 and 2,543,181, issued February 27, 1951; and Yackel et a1. U.S. patent application Serial No. 586,705, filed May 23, 1956 (now US. Patent 3,020,155, issued February 6, 1962). They may also be used in color transfer processes which utilize the diffusion transfer of an image-wise distribution of developer, coupier or dye, from a light-sensitive layer to a second layer, while the two layers are in close proximity to one another. Color processes of this type are described in Land US. Patents 2,559,643, issued July 10, 1951 and 2,698,798, issued January 4, 1955; Land and Rogers Belgian Patents 554,933 and 554,934, granted August 12, 1957; International Polaroid Belgian Patents 554,212, granted July 16, 1957 and 554,935, granted August 12, 1957; Yutzy U.S. Patent 2,756,142, granted July 24, 1956, and Whitmore and Mader U.S. patent application Serial No. 734,141; filed May 9, 1958 (now abandoned). They may also be used in emulsions intended for use in a monobath process such as described in Haist et al. US. Patent 2,875,048, issued February 24, 1959, and in web-type processes, such as the one described in Tregillus et al. U. S. patent application Serial No. 835,473, filed August 24, 1959.

In the preparation of the silver halide dispersions employed for preparing silver halide emulsions, there may be employed as the dispersing agent for the silver halide in its preparation, gelatin or some other colloidal material such as colloidal albumin, a cellulose derivative or a synthetic resin, for instance, a por'vinyl compound. Some colloids which may be used are polyvinyl alcohol or a hydrolyzed polyvinyl acetate as described in Lowe US. Patent 2,286,215, issued June 16, 1942; a far hydrolyzed cellulose ester such as cellulose acetate hydrolyzed to an acetyl content of 1926% as described in U.S. Patent 2,327,808 of Lowe and Clark, issued August 24, 1943; a water-soluble ethanolamine cellulose acetate as described in Yutzy US. Patent 2,322,085, issued June 15, 1943; a polyacrylamide or an imidizec. polyacrylami e as described in Lowe, Minsk and Kenyon US. Patent 2,541,474, issued February 13, 1951; zcin as described in Lowe U.S. Patent 2,563,791, issued August 7, 1951; a vinyl alcohol polymer containing urethane carboxylic acid groups of the type described in Unruh and Smith US. Patent 2,768,154, issued October 23, 1956; or containing cyano-acetyl groups such as the vinyl alcoholvinyl cyanoacetate copolyrner as described in Unruh, Smith and Priest US. Patent 2,808,331, issued October 1, 1957; or a polymeric material which results from polymerizing a protein or a saturated acylated protein with a monomer having a vinyl group as described in US. Patent 2,852,382, of Illingsworth, Dann and Gates, issued September 16, 1958.

If desired, compatible mixtures of two or more of these colloids may be employed for dispersing the silver halide in its preparation. Combinations of these antifoggants, sensitizers, hardeners, etc, may be used.

The antifoggant or stabilizing action of the bis-pyrazole compounds of our invention was determined by incubation of the emulsions for one week (or in some cases for two weeks) at a temperature of 120 F. and constant relative humidity obtained by placing the emulsions in closed containers, the ambient temperature being about 70 F. and relative humidity about prior to scaling the containers.

The elficiency of the various antifoggants was determined by measuring the speed and fog of the incubated emulsions containing an antifoggant and comparing these measurements with those of the same batch of emulsion before incubation. A second series of coatings was made and similar speed and fog measurements made after incubation.

Grams N-methyl-p-aminophenol sulfate 2.5 Hydroquinone 2.5 Sodium sulfite (desiccated) 30.0 Sodium metaborate 10.0 Potassium bromide 0.5

Water to make 1 liter.

The developed testfilms were then fixed, washed and dried in the usual manner. The speed and fog for each of the emulsion coatings were measured as indicated above. The speed figures are given in terms of relative speed numbers and are inversely proportional to the exposure required to produce a density of 0.3 above fog. The results are given in the following tables:

Table I I Fresh 1 Wk. Coating 120 F. Inc. Number Feature Sp Fog Sp. Fog

( n!) Control 100 14 77 21 (b) 3,3,5,5-Tetrarnethy1-4,4-di-py- 80 12 79 .20

razolyl, 0.3 g./n10l. (c) 3,3,5,5-letrametliyl-4,4-di-py- 93 12 83 12 razolyl, 3.0 gJmnl.

Table II I Fresh 2 W12. Coating 120 F. Inc. Number Feature Sp. Fog Sp. Fog

(d) Control 100 14 74 39 (c) 5,5Dlinethyl-3,8-dipyrazolyl, 1.12 .00 05 .30

.75 g./n10l. (f) 5,5Dimetliyl-8,3-d1pymzolyl, 80 10 102 84 3.0 gJmol. (g) 3,3,5,5-'1etrarncthyl-4,4-di-py- 91 .10 117 14 razolyl, 3.0 g./rnnl. Methylei1e-4,4-bis(3,5-dizneth- 107 10 89 .32

yl-pyrazole), .75 g./mol. Methylene-4,4-bis(3,S-dimeth- 01 11 38 .20

yl-pyraznle), 3.0 g./u101.

Table III Fresh 1 Wk. Coating 120 F. Inc. Number Feature Sp. Fog Sp. Fog

(j) Control 100 .13 74 .34 (Ir) 3,3,5,5-Tetraethyl4,4-di-pyraz- 03 12 79 24 yl, 3.0 gJmnl. (l) 3,3,5,5-1etramethy1-4,4-di-py- 100 .14 .22

razolyl, 3.0 g./mo1.

Table IV Fresh 1 W k. Coating 120 F. Inc. Number Feature Sp. Fog Sp. Fog

(m) Control .15 68 .34 (n) 1,1,8,3,5,5-He't:rrnethyl-4,4-di- 72 .13 87 .2'1

pyrazolyl, 3.0 g./mol. (o) 3,3,5,5-1atranmtl|yl-4,4-di-py- 100 12 95 17 razolyl, 3.0 glinol.

As indicated above, the bis-pyrazole compounds of our invention are markedly superior to the monopyrazole compound previously suggested in the prior art as antifoggants or stabilizers. The following tables show the marked improvement provided by our bis-pyrazole compounds over chemically related structures which contain a single heterocyclic ring. The coatings were made and processed exactly as described above with respect to Tables I-V.

Table A (loat- Fresh 1 Week 120 F. Inc.

mg Num- Feature ber Speed Gam- Fog Speed Gam- Fog ma ma Es)..-" Control 100 1.13 .15 94 0.98 .33

t) 3,3,5,5-'Ietramethyl- 4,4-dipyrazolyl, .9 gJmoLAgX 100 1.20 .11 112 1.08 .20 (11)..." 3,3,5 -'letramethyl- 4,4 -dipyrazoly1, 3.0 gJmoLAgX 100 1.25 .10 115 1.12 .13 (u)- Phthalimide, .9

01. 110 1.23 .12 95 1.00 .26 (w) Phthelimide,30

gJmOl. AgX 115 1. 30 .11 102 1.12 .22 (z) Phthalimide, 9.0

gJmOLAgX 118 1.33 .12 97 1.15 .29 (y). Saccharin (o benzoic sulfiruide Na salt), .9 g./mol. AgX 107 1.17 .11 95 0.97 .21 (z) Saccharin (0benzoic sulfimide Na salt), 3.0 g./m0l. AgX.. 110 1.22 11 95 0.98 .23 (a). Saccharln (o-benzoic sulfunlde Na salt), 9.0 g./m0l.AgX 105 1.17 .11 100 1.02 .19 (b) Succluimide, .9 g./m01.

AgX 107 1.17 .11 94 0.95 .26 (c) Suctinimide, 3.0

gJmol. AgX 100 1.15 .11 94 0.98 .26 (d') Succinimide, 9.0 v

gJmol. AgX 97 1.13 .10 94 0.93 .28

Table B Coat- Fresh 1 Week 120 F. Inc.

Num- Feature ber Speed Gam- Fog Speed Gam- Fog 111a ma (6%---. Control 100 1.23 .13 76 1.07 .21 (f 1,3,5-trimethyl-pyraz0le,3.0g./m01.AgX 94. 1.12 .13 97 1.27 .20

Table C Goat- Fresh 1 Week 120 F. Inc. mg Num- Feature ber Speed Gam- Fog Speed Gam- Fog ma ma (g') Control 100 .11 78 .19 (h) 3,5-D1methyl-pyrazole,

3.0 g./m0l. AgX 102 12 73 .20

The optimum amount of fog-inhibiting agent can be determined by making the customary tests employed in emulsion making. Of course, the optimum amount for a given emulsion will vary depending on the presence of emulsion addenda, such as chemical sensitizers, optical sensitizers, etc. In general, we have found that from 0.1

. 10 to 5.0 g. of fog-inhibiting agent per mole of silver halide is sufficient for the purposes of our invention.

Instead of adding the fog inhibiting agent directly to the photographic emulsion, it is sometimes desirable to incorporate the fog-inhibiting agent in a separate layer which is placed in contact with the silver halide emulsion layer which is to be stabilized. Under such conditions, of course, it is advisable to use a higher concentration of fog-inhibiting agent than indicated above. The antifoggants of our invention function advantageously in acid or alkaline photographic silver halide emulsions.

The invention has been described in detail with particular reference to preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention as described hereinabove and as defined in the appended claims.

What we claim as our invention and desire secured by Letters Patent of the United States is:

1. A photographic element comprising a support, a water-permeable hydrophilic silver halide emulsion layer and in contiguity with said silver halide emulsion layer,

a water-permeable hydrophilic colloid layer, at least one of said water-permeable hydrophilic colloid layers containing a compound selected from those represented by the following general formula:

' wherein R represents an alkylene group, R R and R each represents a member selected from the class consisting of a hydrogen atom and a lower alkyl group, and n represents a positive integer of from 1 to 2.

2. A photographic element comprising a support, a water-permeable hydrophilic silver halide emulsion layer and in contiguity with said silver halide emulsion layer, a water-permeable hydrophilic colloid layer, at least one of said water-permeable hydrophilic colloid layers containing a compound selected from those represented by the following general formula:

\C(R1) n-1-C R3-N-N N-N-R wherein R represents an alkylene group, R and-R each represents a member selected from the class consisting of a hydrogen atom and a lower alkyl group, and n represents a positive integer of from 1 to 2.

3. A photographic silver halide emulsion containing a stabilizing amount of a compound selected from those represented by the following general formula:

wherein R represents an alkyleue group, R R and R each represents a member selected from the class consisting of a hydrogen atom and a lower alkyl group, and n represents a positive integer of from 1 to 2.

4. A photographic silver halide emulsion containing a stabilizing amount of a compound selected from those represented by the following general formula:

wherein R represents an alkylene group, R and R each 1 1 represents a member selected from the class consisting of a hydrogen atom and a lower alkyl group, and n represents a positive integer of from 1 to 2.

5. A photographic silver halide emulsion containing a stabilizing amount of 3,3,5,5-tetraethyl-4,4-bipyraz0lyl.

6. A photographic silver halide emulsion containing a stabilizing amount of 5,5-dimethyl-3,3-bipyrazolyl.

7. A photographic silver halide emulsion containing a stabilizing amount of l,l',3,3,5,5'-hexan1ethyl-4,4-bipyrazolyl.

8. A photographic silver halide emulsion containing a stabilizing amount of 1,1,5,5'-tetramethyl-3,3-bipyrazolyl.

9. A photographic silver halide emulsion containing a 12 stabilizing amount of methylene-4,4-bis(3,5-dimethylpyrazolc).

References Cited in the file of this patent UNITED STATES PATENTS 1,763,989 Sheppard et al June 17, 1930 2,588,538 Kendall et al Mar. 11, 1952 3,040,047 Sirakawa June 19, 1962 FOREIGN PATENTS 850,382 Germany Sept. 25, 1952 OTHER REFERENCES Reirnlinger: Chem. Ber., vol. 92, pp. 9707, 1959. 

1. A PHOTOGRAPHIC ELEMENT COMPRISING A SUPPORT, A WATER-PERMEABLE HYDROPHILIC SILVER HALIDE EMULSION LAYER AND IN CONTIGUITY WITH SAID SILVER HALIDE EMULSION LAYER, A WATER-PERMEABLE HYDROPHILIC COLLOID LAYER, AT LEAST ONE OF SAID WATER-PERMEABLE HYDROPHILIC COLLOID LAYER CONTANING A COMPOUND SELECTED FROM THOSE REPRESENTED BY THE FOLLOWING GENERAL FORMULA 